Modern vehicles and in particular hybrid or electric vehicles, have onboard power supply systems that comprise a high voltage onboard power supply system path in which an operating voltage of several hundred volts prevails.
A voltage of over 60 volts is life threatening for human beings, particularly for children, however. Therefore, a high voltage onboard power supply system path having an operating voltage of more than 60 volts is electrically insulated from the remainder of the onboard power supply system or from the vehicle bodywork in order to eliminate a threat to human beings.
If there are technical failures in the onboard power supply system or in the event of operating errors, what is known as a fault current can flow through the human body from the high voltage onboard power supply system path. If the electrical insulation between said high voltage onboard power supply system path and the remainder of the onboard power supply system or the vehicle bodywork is intact and sufficiently high at that time, then the amperage of the fault current is limited to a value that is not hazardous to human beings.
If the electrical insulation is not sufficiently high, however, then a fault current having an amperage of several milliamps can flow through human bodies, which can be life threatening to human beings.
In order to avoid such life-threatening fault currents from the outset, it is necessary to monitor the electrical insulation in the onboard power supply system continually and to identify potential hazards as early as possible.